2/28: I invented a way to toss a tennis ball straight up. (North Park)

I invented a way to toss a tennis ball straight up.
A bad toss is far and away the main reason for bad servers, like a batter chasing bad pitches.
I want six people with a bad tennis serve to learn the method (15-30 minutes) and thereafter shoot a very short head shot testimonial video – 2-3 sentences, informal and anonymous, at North Park Rec Center – stating how well their serve improved.
The date is listed as 2/28 but we can arrange a different day/time per your schedule.
There's no catch.
This is all it is.
There's no payment or sales pitch.
I have no lessons to sell.
Randy Zeitman, North Park I am also a member at Balboa if that's more convenient.